In a discussion with a friend in which I was attempting to explain the primacy of examining presuppositions, he noted that he likes to empirically establish the historicity of Scriptural events rather than delve into the philosophical. He asked for my thoughts, and I think that my response can serve as a specific example of a general point; namely, that accepting another’s presuppositions for the sake of argument in order to show that “Christianity is probable even within another person’s world-view” may be more trouble than its worth:
“Insofar as you are seemingly working within the framework of empiricism, while it may be useful to show that even within an unsound world-view Christianity is probable, your arguments will invariably be suspect to the same criticisms which stem from the unsound presuppositions of said world-view. One such criticism immediately comes to mine: what constitutes historical reliability? Unless you can answer this question, talk of "probability" is nonsensical, and yet trying to justify your criterion will beg more questions than you may want to answer.
Now, if you and a secular historian can come to an agreement on this and other similar questions, then your arguments will obviously have more force and, to that end, your method can be useful. But I would not be honest if I recommended it to you. Instead, I prefer a more direct method, one which avoids induction and the like, a method which, epistemologically speaking, gets to the root of the issue: presuppositions, axioms, or first principles. I would utilize your method as an "even if" scenario, e.g. "even if your presuppositions are sound, look at where the evidence points." More often than not, however, I think that this does more harm than good, as it may give another the false impression that a concession is being made regarding the soundness of said presuppositions.”
I could have added that an outsider looking in may enter into the conversation and fault both parties for relying on flawed presuppositions, causing a messy situation in which the Christian must explain that he is only accepting the presuppositions for the sake of argument. Things get confusing. To elaborate a little further on my preferred method, what I mean to say is that dialogue and dividing lines can be much more clear if we simply critique the internal consistency of another's presuppositions or first principles and discarding whichever yields contradictions (reductio ad absurdum). Or, as Gordon Clark wrote:
“The argument is ad hominem and elenctic. When finally the opponent is reduced to silence and we can get in a word edgewise, we present the word of God and pray that God cause him to believe.”